The fixative designated 4CF-1G consists mainly of which aldehydes?

• A. Formaldehyde and glutaraldehyde.
• B. Formaldehyde and picric acid.
• C. Osmium tetroxide and formaldehyde.
• D. Formaldehyde and methanol.

Answer: (A)

The main idea is that this fixative uses two aldehydes to crosslink proteins and lock cellular structures in place. Formaldehyde is a small aldehyde that penetrates quickly and forms methylene bridges between amino groups on proteins, giving rapid fixation of overall tissue structure. Glutaraldehyde is a larger dialdehyde that creates more extensive crosslinks, providing excellent preservation of fine ultrastructural detail. Using both together gives fast penetration plus strong, durable crosslinking, which is why this combination is chosen for reliable fixation.

The other options aren’t aldehydes (picric acid is a nitro compound used as a precipitating fixative, osmium tetroxide is an oxidizer used for lipid preservation and staining, and methanol is an alcohol), so they don’t represent the aldehydes in this fixative.